Numerous extrusion plates are currently known for the production either of hollow fibers or membranes comprising a plurality of separate longitudinal passages. Such extrusion plates are especially described in the U.S. Pat. No(s). A-3,081,490 and A-3,075,242 (hollow fibers), German patent A-3,022,313; Swiss patent A-516,985 and U.S. Pat. No. A-2,965,925 (membranes provided with a plurality of passageways) and comprising at least one needle on the interior of which is introduced a centering fluid, and an interstitial volume around that (or those) needles in which a polymeric solution flows. While these extrusion plates present their own particular qualities, they all have some common disadvantages. They are all of a rather high cost either by reason of the complexity of their constituent elements, or by reason of a high number of such constituent elements needed for their production. Further, the time of duration of the fluids on the interior of these extrusion plates is generally long and produces heat exchange between the fluids which leads to the formation of a particular, predefined structure of the polymeric material. Finally, these extrusion plates have dead zones which makes their cleaning difficult and generally requires dismantling them for cleaning. These dead zones constitute further spaces in which air pockets may form during extrusion of the membrane.
The present invention seeks to overcome these disadvantages of known extrusion plates and has as the primary objective to provide an extrusion plate produced from a reduced number of pieces each having a simple structure.
Another object of the invention is to provide an extrusion plate able to be cleaned without disassembly.
Another object is to provide an extrusion plate in which the time of duration of fluids therein is as short as possible.
Another object is to provide an extrusion plate having no dead zones in the direction of fluid flow.